The present invention relates to an apparatus for converting one type of motion to another type of motion, and more particularly, to an apparatus for converting rotary motion to linear motion.
The prior art has employed various types of apparatuses and arrangements for converting rotary motion to linear motion. One type of arrangement includes a plurality of roller members that surround a centrally located and externally threaded screw. The roller members have flanges that extend radially outward from the exterior surface thereof and which engage the thread on the outer surface of the screw. Further, a ring encircles the roller members and the screw whereby the roller members are positioned between the screw and the ring. Prior art apparatuses similar to that described above are disclosed in U.S. Pat. Nos. 4,048,867, 4,050,319, 4,576,057, 3,884,090 and 4,655,100.
However, the prior art assemblies described above fail to take into account the relationship between the outer diameter of the screw and the outer diameter of the roller members and the affect that relationship has on the bearing stresses produced in the screw assembly. Since the bearing stress in the screw assembly affects the performance and operation of the screw assembly, the relationship between the diameter of the screw and the diameter of the roller members should be taken into consideration when designing the screw assembly.
The prior art screw assemblies also fail to consider the affect that the canted load bearing surfaces of the screw, the roller members and the ring have on the behavior of the screw assembly. In that respect, the prior art does not recognize that the canted load bearing surfaces of the various rotating parts of the screw assembly tend to produce an effective radius for each of the rotating parts that is larger than the respective actual radii. Thus, the prior art does not realize that the rolling parts behave as though they have larger radii of curvature.